Queenborough Castle, also known as Sheppey Castle, is a 14th-century castle, the remnants of which are in the town of Queenborough on the Isle of Sheppey, Kent in England. The castle and the associated planned town were built on the orders of King Edward III from 1361 and named in honour his wife, Queen Philippa. It was the first concentric castle to be built in England, and the only royal castle to be new-built in England during the Late Middle Ages. Overlooking the Swale, then an important waterway approaching the River Medway, Queenborough Castle formed part of the country's coastal defences until 1650 when it was declared to be unfit for use and was almost completely demolished shortly afterwards. The site is now a public park and the only visible remains are some low earthworks.